There are certainly a lot of similar sounding posts in this forum, but I haven’t seen any that touch on this issue directly. I submitted a support ticket to Particle, but wanted to share with the community to see if anyone else has had success digging into this problem (and hopefully finding a workaround!).

I’ve been seeing an issue intermittently across at least 6 devices in our “fleet” of 50 Electron units over the past year. In scenarios I have not yet been able to reproduce, the Electron will not charge the connected LiPo battery until the USB connector has been unplugged and plugged back in a number of times. Obviously this is a big headache when these service-critical devices are deployed and can only be charged overnight. To remedy this challenge I have actually built in an external 500mA charger onto the backplane board in future builds and will disable onboard PMIC charging… but I really don’t love this solution.

I finally caught a device which was doing this in the shop and was able to dig in a little deeper (though by no means did I resolve the issue). Here’s the process I went through, in as much detail as possible:

Noticed charge light was not illuminated on the Electron, despite being plugged in to a 5V,2A wall charger overnight

Measured battery voltage with a multimeter (probed the BAT pin on the device) and saw it was around 3.25V

Plugged unit into my laptop with a charge monitor and confirmed negligible current was going to the device

Wrote a test program to output all available fuel gauge and PMIC data:

NOTE: When I loaded this firmware onto the device, I had not noticed the build environment was set to Device OS v1.0.0 (the Device OS running on the Electron at the time was 0.8.0-rc.4). The issue persisted across the automatic Device OS update (and we have seen it with devices running v0.7.0)

So, what’s curious is the Status Register, which (referring to the BQ24195 datasheet) is indicating VBUS is unknown. However, I was still able to program the Electron

At this point, out of curiosity, I unplugged the battery while leaving the Electron plugged into USB. All power to the board extinguished. Thinking it may be a micro USB connector issue, I measured the voltage to the VUSB/VBUS pin with a multimeter and it measured at 5V. So 5V is presumably still getting to the PMIC.

With the battery still unplugged, I unplugged and plugged in the USB connector (from my laptop) several times. Suddenly, the board revived. The charge LED rapidly blinked for a few seconds and then turned off (which I think is odd, because that light should keep blinking until a battery is connected)